I am starting to think that the factor to which people react is glutathione precursors (glutamic acid + sulfur), because I love eating meat and flax made me very ill. My understanding was that flax "freezes" glutamic acid avoiding its conversion to either glutamate or glutathione.
As I posted elsewhere, I felt that flaxseed oil inhibited glutathione synthesis by blocking thyroid hormone receptors, or T3 synthesis. I suppose this would hit harder those with thyroid problems like myself.
So for some people eating meat makes it easier to make glutathione, for other it becomes harder and they get increased glutamate and sulfites (ammonia?)
If the problem is ammonia, then Biotin should help with that.
Glutathione synthesis requires sufficient glycine, cysteine, and glutamine. If you have too much of one, and not enough of the others, you will be limited in the amount you make. Excess glutamine, can be used elsewhere, which can create symptoms. Many of us need glycine and NAC, n-acetyl-cysteine, to use the glutamine to make glutathione.
Glutathione must be recycled, so you need adequate vitamin C to do that. It also helps in detoxification, sending toxins through the transsulfuration pathway. If one is short of B1 and/or molybdenum, one may have a sulfur problem. B6 is needed, too.
I tend toward high sulfur. We've found I need large doses of B6, so I'm on that. When I start emitting sulfur, I up my molybdenum and B1, while taking activated charcoal away from other supplements to bind it. Curcumin helps too.
High ammonia is not the same as high sulfur. Glutathione, milk thistle, garlic, arginine, ornithine, and lysine can help diminish it.
I have thyroid problems too, but find that keeping my nutrient levels sufficient minimizes my other issues.